Glass laminated products have contributed to society for almost a century. Beyond the well known, every day automotive safety glass used in windshields, laminated glass is used in all forms of the transportation industry. Safety glass is characterized by high impact and penetration resistance and does not scatter glass shards and debris when shattered.
Safety glass typically consists of a sandwich of two glass sheets or panels bonded together with an interlayer of a polymeric sheet. One or both of the glass sheets may be replaced with optically clear rigid polymeric sheets, such as sheets made of polycarbonates. Safety glass has further evolved to include multiple layers of glass and polymeric sheets bonded together with interlayers of polymeric sheets.
The interlayers used in safety glass are typically made from relatively thick polymer sheets, which exhibit toughness and bondability to the glass in the event of a crack or crash. Widely used interlayer materials include complex, multicomponent compositions based on poly(vinyl butyral) (PVB), poly(urethane) (PU), poly(ethylene vinyl acetate) (EVA), ionomers, and the like.
As a renewable energy resource, the use of solar cell modules is rapidly expanding. One preferred way of manufacturing a solar cell module involves forming a pre-laminate assembly comprising at least 5 structural layers. The solar cell pre-laminates are constructed in the following order starting from the top, or incident layer (that is, the layer first contacted by light) and continuing to the backing (the layer furthest removed from the incident layer): (1) incident layer (typically a glass plate or a thin polymeric film (such as a fluoropolymer or polyester film), but could conceivably be any material that is transparent to sunlight), (2) front encapsulant layer, (3) voltage-generating component (or solar cell component), (4) back encapsulant layer, and (5) backing layer.
The encapsulant layers are designed to encapsulate and protect the fragile voltage-generating component. Generally, a solar cell pre-laminate will incorporate at least two encapsulant layers sandwiched around the solar cell component. The optical properties of the front encapsulant layer must be such that light can be effectively transmitted to the solar cell component. Additionally, encapsulant layers generally have similar requirements and compositions to that described above for glazing interlayers.
The use of ionomeric compositions as threat resistant safety laminate interlayer sheets has been known within the art (see, e.g. U.S. Pat. No. 3,344,014; U.S. Pat. No. 3,762,988; U.S. Pat. No. 4,663,228; U.S. Pat. No. 4,668,574; U.S. Pat. No. 4,799,346; U.S. Pat. No. 5,759,698; U.S. Pat. No. 5,763,062; U.S. Pat. No. 5,895,721; U.S. Pat. No. 6,150,028; U.S. Pat. No. 6,432,522; US 2002/0155302; US 2002/0155302; WO 99/58334; and WO 2006/057771). For Example, U.S. Pat. No. 5,759,698 discloses a glass laminate interlayer derived from an ionomer resin which has been thermoset with an organic peroxide and a silane agent.
The use of ionomeric compositions as solar cell encapsulant films or sheets has also been known within the art (see, e.g., U.S. Pat. No. 5,476,553; U.S. Pat. No. 5,478,402; U.S. Pat. No. 5,733,382; U.S. Pat. No. 5,762,720; U.S. Pat. No. 5,986,203; U.S. Pat. No. 6,114,046; U.S. Pat. No. 6,187,448; U.S. Pat. No. 6,660,930; US 2003/0000568; US 2005/0279401; JP 2000186114; and JP 2006032308).
However, the ionomeric resins being used in the art of safety laminates or solar cell modules generally have a low melt flow index (MI) of 15 g/10 min or less (2160 g, 190° C., ISO 1133, ASTM D1238). The use of such low melt flow ionomeric resins requires higher lamination temperatures (i.e., 130° C.-170° C.) and therefore may complicate the lamination process.
Chou et al., in U.S. Pat. No. 6,680,821, describe a method of coating a metallic surface using a resin powder comprising certain metal neutralized acid copolymers comprising an alpha-olefin and an alpha-beta unsaturated carboxylic acid with a MI in the range of from about 20 to about 1,000 g/10 min. This patent does not describe use of such materials within safety glass or photovoltaic module laminates or additive packages that enhance the performance of the copolymers in such uses.
There is a need for polymeric film or sheet suitable for use as interlayers in glass laminate end-use applications, such as safety windows and solar cells, that do not have the shortcomings described above, as well as for compositions useful in forming such films or sheets. For instance, there is a desire to prepare useful compositions with a reduced extrusion compounding temperature. In addition, there is a desire to reduce the lamination temperature, preferably to about 100° C. to about 120° C., or to reduce the lamination cycle time, or both, and therefore simplifying the lamination process. In addition, there is a desire for films or sheets that have enhanced adhesion strength under a wide variety of lamination temperatures, including such desirable lower temperatures, and to provide the laminates with improved shock resistance.